In our research group, the project, named "networked robotic system for disaster mitigation", has been carried out to perform robotic victim-search in disaster environment. In this project, we have developed a mobile robots' system which consists of small mobile robots (to search victims in collapsed buildings) and a large-mobile-robot (to convey small robots into it). In order to approach to the target buildings, the large robot is required to surmount some debris and bumpy terrain. For this purpose, the robot has six wheels, and two pairs of wheels in front are formed as actuated rocker structures. This wheel configuration can achieve "active load-equalizer" or other control methods by using load cell data. In this paper, the system description and control methods of the large robot are introduced. We also report a performance of the control methods using a "robot dynamics simulator" developed in our group and preliminary experiments using real robot to evaluate the feasibility of our approach.